The invention relates generally to materials and devices used in the detection of ionizing radiation. More specifically, it relates to scintillator compositions, which are especially useful for detecting gamma-rays and X-rays under a variety of conditions.
Many techniques are available for detecting high-energy radiation. Scintillators are of special interest, in view of their simplicity and accuracy. Thus, scintillator crystals are widely used in detectors for gamma-rays, X-rays, cosmic rays, and particles characterized by an energy level of greater than about 1 keV. From such crystals, it is possible to manufacture detectors, in which the crystal is coupled with a light-detection means, i.e., a photodetector. When photons from a radionuclide source impact the crystal, the crystal emits light. The photodetector produces an electrical signal proportional to the number of light pulses received, and to their intensity. Scintillator crystals are in common use for many applications. Examples include medical imaging equipment, e.g., positron emission tomography (PET) devices; well-logging for the oil and gas industry, and various digital imaging applications.
Scintillators are designed to be responsive to X-ray and gamma ray excitation. Moreover, it is desirable that scintillators possess a number of characteristics which enhance radiation detection. For example, scintillator materials desirably possess high light output, short decay time, high “stopping power”, and acceptable energy resolution.
Commonly used scintillator materials include thallium-activated sodium iodide (NaI(Tl)), bismuth germanate (BGO), cerium-doped gadolinium orthosilicate (GSO), and cerium-doped lutetium orthosilicate (LSO). Although, each of these materials has some good properties which are suitable for certain applications, they possess one or more deficiencies, along with their attributes. Deficiencies may include low light conversion, slow decay time, an emission spectrum not spectrally matched to the photodetector, large temperature dependency of sensitivity, low x-ray or gamma-ray stopping power, or absorption of oxygen and moisture leading to persistent afterglow and high background rate due to radioactive isotope of component elements.
New scintillator materials that exhibit excellent light output, as well as relatively fast decay times are therefore desirable. They should also desirably possess good energy resolution characteristics, especially in the case of gamma rays. Moreover, new scintillators should desirably be readily transformable into single crystalline materials or other transparent solid bodies. Furthermore, they should desirably be capable of being produced efficiently, at reasonable cost and acceptable crystal size. The scintillators should also desirably be compatible with a variety of high-energy radiation detectors.